The invention relates to a process for the preparation of aromatic hydrocarbons and hydrogen from a paraffin with four carbon atoms in the molecule (a C.sub.4 paraffin) or from a hydrocarbon mixture which consists of more than 75% w paraffins with at most four carbon atoms in the molecule (C.sub.4- paraffins) and more than 50% w C.sub.4 paraffins, using a crystalline silicate as the catalyst.
In an investigation by Applicants concerning the abovementioned process it has been found that the activity, the aromatics selectivity and the hydrogen selectivity of these crystalline silicate catalysts are greatly dependent on the value of y in the formula which gives the overall composition of the silicate, are further dependent on the metal promoter which has been deposited on the silicate and are dependent upon the pressure used in the process. It was found that to reach an activity, an aromatics selectivity and a hydrogen selectivity which are acceptable for commercial use of the process, y should be at most 0.01, the silicate should contain zinc as the promoter and the process should be carried out at a pressure below 5 bar.